The anonymous user wrote that his wife saw the knife and went into the next car to try to alert the train operator. Meanwhile, the user claimed he pushed the emergency call button.

"This almost cost me my life, as in the time it took for me to stand up and hit the button, the assailant had walked up to me. It was only once he got close that I saw the knife. He told me to shut up, which I did, raising my hands," the Reddit user wrote.

The Reddit post said the suspect then robbed two people, which was also mentioned in court documents released Tuesday. The victim was stabbed or cut 30 to 40 times, authorities said.

"He then assaulted Kevin again, and when the train pulled up to the station, got off," the post said.

The Reddit user's wife called 911 and relayed instructions to passengers exiting the train, according to the post. The user wrote that he stayed on the train to sit with Sutherland in hopes of keeping him conscious.

"I sat with Kevin, held his hand, stroked his head and kept telling him to breathe, and that he was going to see the fireworks next year. I sat with him until he died," he wrote.

In the wake of the tragedy, the user wrote that he wished he had some kind of emergency first aid training that may have helped the victim.

"I know, intellectually, that his wounds were far too bad for it to have probably made a difference, but this is what is going to haunt me for a long time," the Reddit user wrote. "I am lucky to be alive. But Kevin is not, and my heart breaks every time I think about it."

FOX 5 has reached out to the Reddit user, but we have not been able to independently verify the story.